How to enable an addon on startup via script?
You can enable a comma-separated list of addons through the command line/terminal, so you're able to do that through a script. That functionality is described in the blender terminal help (./blender --help). 

An example would be ./blender -b --addons animation_nodes,meshlint [file] to enable animation nodes and meshlint, then load your file.

If you need to load a single python script, such as a set of operations you want to use on a mesh object, you can use the --python flag. ./blender -b --addons animation_nodes,meshlint [file] --python [myscript.py] loads blender in the background, loads specified addons, loads the file, then executes the python script.

Unfortunately, the wiki is not helpful here; it only goes over basic rendering functionality. Simply call the help flag to see everything the executable can do from the terminal. A specific thing to remember is that flags are order-sensitive. Those flags listed first will be interpreted first, sequentially until the end of the command.